The topography of the thalamic projections to the trunk representation zone of the first somatosensory area (SI) was studied in the cat by performing experiments of retrograde neuronal tracing. Single injections of horseradish peroxidase or fluorescent tracers (Evans Blue, Nuclear Yellow, Fast Blue) in area SI resulted in retrograde labelling of cell aggregates in the dorsal region of the nucleus ventralis postero-lateralis (VPL) intervening between the lateral (VPLl) and medial (VPLm) subnucleus. The aggregates of labelled cells were elongated rostrocaudally in VPL but were narrow in the dorsoventral and mediolateral extent. In separate experiments, physiologically defined sites of the trunk zone, corresponding to the representation of the dorsal midline, lateral trunk and ventral midline, were injected with different fluorescent markers. The three sites were located in rostrocaudal sequence in the medial part of area SI and corresponded, in the order, to the cytoarchitectonie fields 3b, 1, 2. In these animals three different cell aggregates were labelled, orderly located in topographically distinct regions of VPL trunk zone. According to these results, adjacent cortical foci disposed in rostrocaudal sequence in area SI receive thalamic projections from adjacent neuronal aggregates located in lateromedial sequence in VPL. Each aggregate had a focal projection to a single cortical region since no double-labelled cells were found in VPL.
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Con il contributo del Ministero per i Beni e le Attività Culturali